"More things sound more fun to do, because the kids remind you to play make believe and that's what we are doing. If we do it well, we make you believe."

Sporting a black cowboy hat, jeans and cowboy boots at Austin's South By Southwest film and music festival (which runs through March 18), McConaughey stepped out of a party bus with fiancée Camila Alves, family members and friends for Saturday night's premiere of Killer Joe – and shared a long kiss with his bride-to-be before the film.

The dark comedy, directed by William Friedkin (The Exorcist), stars McConaughey as a Dallas police officer who moonlights as a hired killer.

"When I read the script the first time, I put it down and was disgusted by it," McConaughey, 42, tells PEOPLE. "I didn't want to be around those people. I picked it up again when I had my tickle bone on, and all of a sudden got the humor of it."

Costar Gina Gershon tells PEOPLE, "The movie is out there and it is pretty hard core."

Having moved to Austin with Alves and their two children, Levi and Vida, four months ago, McConaughey told reporters he feels like he's home.

"Austin is more of an identity town than it is an industry town," he says. "It feels good to be back home. It feels good to have my family here, my kids here."